British Astronomical Association Variable Star Section Circular No 77, August 1993 ISSN 0267-9272 Office: Burlington House, Piccadilly, London, W1V 9AG Section Officers Director Tristram Brelstaff, 3 Malvern Court, Addington Road, Reading, Berks, RG1 5PL Tel: 0734-268981 Assistant Director Storm R Dunlop 140 Stocks Lane, East Wittering, Chichester, West Sussex, P020 8NT Tel: 0243-670354 Telex: 9312134138 (SD G) Email: CompuServe:100015,1610 JANET:SDUNLOP@UK. AC. SUSSEX.STARLINK Secretary Melvyn D Taylor, 17 Cross Lane, Wakefield, West Yorks, WF2 8DA Tel: 0924-374651 Chart John Toone, Hillside View, 17 Ashdale Road, Secretary Cressage, Shrewsbury, SY5 6DT Tel: 0952-510794 Nova/Supernova Guy M Hurst, 16 Westminster Close, Kempshott Rise, Secretary Basingstoke, Hants, RG22 4PP Tel & Fax: 0256-471074 Telex: 9312111261 (TA G) Email: Telecom Gold:10074:MIK2885 STARLINK:RLSAC::GMH JANET:GMH0UK. AC. RUTHERFORD.STARLINK. ASTROPHYSICS Pro-Am Liaison Roger D Pickard, 28 Appletons, Hadlow, Kent, TN11 0DT Committee Tel: 0732-850663 Secretary Email: JANET:RDP0UK.AC.UKC.STAR STARLINK:KENVAD: :RDP Computer Dave McAdam, 33 Wrekin View, Madeley, Telford, Secretary Shropshire, TF7 5HZ Tel: 0952-432048 Email: Telecom Gold 10087:YQQ587 Eclipsing Binary Director Secretary Circulars Editor Director Circulars Assistant Director Subscriptions Telephone Alert Numbers Nova and Supernova First phone Nova/Supernova Secretary. If only Discoveries answering machine response then try the following: Denis Buczynski 0524-68530 Glyn Marsh 0772-690502 Martin Mobberley 0245-475297 (weekdays) 0284-828431 (weekends) Variable Star Gary Poyner 021-3504312 Alerts Email: JANET:[email protected] STARLINK:BHVAD::GP For subscription rates and charges for charts and other publications see inside back cover Forthcoming Variable Star Meeting in Cambridge Jonathan Shanklin says that the Cambridge University Astronomical Society is planning a one-day meeting on the subject of variable stars to be held in Cambridge on Saturday, 19th February 1994. Further details will be published in VSS Circulars, in the BAA Newsletter and in Astronomy Now when the arrange­ ments have been finalised. Editorial Some of you may be rather mystified by Mike Carson-Rowland's article in this issue. In it he describes some of his experiences typing up observations as part of the VSS Computerisation Project. By using various short-cuts, he has been able to greatly speed up the rate at which he can enter the observ­ ations. The details he gives are specific to the word-processor that he uses but the overall ideas should be more generally applicable. However, don't assume that you have to understand all that Mike says to be able to help with data entry - Herbert Joy is still getting along very well without all of these tricks, using a very simple word-processor on an ancient BBC Micro! Adding Stars to the Program Shaun Albrighton, after discussions with Mike Gainsford, suggests that we could add some of the recently discovered red variables to the Program to replace those binocular stars that have been and that are likely to be dropped. He also points out that there is a marked lack of dwarf novae in the spring sky and a lack of Mira's and semiregulars in the summer sky. The Director agrees that some of Mike Collins' red variables would make good additions to the Program, however, most of them are fainter than mag 8.5 and so are more suited to small telescopes than binoculars. Charts for many of these stars can be found in back issues of The Astronomer. Has anyone been observing any of them visually? It would be useful to have some idea of the visual range and level of activity of any stars before we comitted ourselves to observing them long-term. Also, it would be nice to pick some stars for which there already exists at least one dedicated observer and a reasonable run of estimates. If you have any suggestions then please send them to the Director. V1016 Orionis (= Theta 1 Ori A) Apologies to A Viertel of Germany and to any one else who tried to observe the eclipse of V1016 Orionis which, in VSS 75, was predicted for March 14/15. This should have read February 14/15. I should have checked the prediction against the Krakow Yearbook. The following list gives the minima of this star which should be observable from Britain over the next couple of years. The times are GMAT and the format is similar to that used in the main eclips­ ing binary predictions elsewhere in this Circular. Mark these dates on your calendar. Even fragmentary observations of these eclipses could be useful. 1993 Nov 3 Wed L10(06)15 1994 Nov 30 Wed 11(20)17L 1994 Jan 7 Fri 07(16)15L 1995 Feb 4 Sat D06(06)13L 1994 Mar 14 Mon D07(02)10L 1995 Apr 10 Mon D08(17)09L 1994 Sep 26 Mon L13(10)17D 1995 Aug 19 Sat L15(13)16D Erratum Apologies to Graham Pointer for calling him 'Gary' on page 4 of VSSC 76. STERNWARTE SONNEBERG Sonnebercr Observatory threatened 'To many astronomers, the name of Sonneberg Observatory is synonymous with variable star research and its importance can hardly be over-estimated. The Sky Patrol has been operating since 1926, and the huge collection of plates forms an indispensable archive and source of data, recently described in ESO's "The Messenger' 68 (1992 Jun), p24-26. The importance of maintaining the archive has been recognized by a recent resolution of the IAU Commissions 27 and 42 (IAU Inf. Bull. 67, 39-40, 1992). There is also a pool of expertise among the staff, which is less easily quantified, but nonetheless of major importance for the study of variable stars. Sonneberg is now threatened with closure in 1994. Those professional and amateur astronomers who wish to protest against this action should contact the special group that has been formed to fight for the observatory's survival: Freunde der Sternwarte Sonneberg, Sternwarte Sonneberg, Sternwartestrasse 32, DO-6400 Sonneberg, Germany.' Storm Dunlop wrote the above piece which has also appeared in other public­ ations. He is right when he says the importance of the observatory can hardly be over-estimated: the collection of over 240,000 plates is second only to the Harvard collection(400,000) and in some respects (continuity and accessibility) it is superior. Our knowledge of the historical variations of many of the most important variable stars is heaviliy dependent on the Sonneberg plate collection: the X-ray star HZ Her, V651 Mon (the central star of the planetary nebula NGC 2346), the unique object FG Sge, and the quasar 3C273, to name just a few. Robert McNaught's 'rediscovery' of VY Aqr was followed up at Sonneberg by Wenzel and Richter who found several historical outbursts which had previously gone undetected. A quick glance at the IBVS summaries in this Circular will show that Wenzel is, even now, continually producing new and interesting results using the plate collection. 2 Recent UBVR Magnitudes for Rho. V509 and Tau Cas In Information Bulletins on Variable Stars No's 3848, 3849 and 3851, Elaine Halbedel presents photoelectric measures of these three stars made at the Corralitos Observatory in New Mexico, USA. These are part of a continuing series of observations of the semiregular supergiant variables Rho and V509 Cas. She uses her observations and some from other sources to construct the accompanying light-curves. In observing Rho she used Tau as a comparison star. Tau has actually been suspected of variability by visual observers but, according to Percy, this has not been confirmed by photoelectric observ­ ations. Indeed, up until 1990 Halbedel's measures showed Tau to be constant to within a few hundreths of a magnitude relative to the check star (HR 9010). However, in 1991 and 1992 it was recorded about 0.05 mag brighter than normal (see light-curve). Halbedel points out that it is not yet completely definite that Tau is the source of the apparent variation - it could possibly be the check star or it could be due to atmospheric effects (eg: the Mount Pinatubo eruption), although the latter is unlikely as nothing similar is shown by any other stars on the Corralitos observing program. Geminga Again In Nature (364, 395-396, 1993), Priscilla Frisch of the University pf Chicago presents a convincing case for the Geminga supernova (see VSSC 76, page 6) having occurred within the Orion association rather than close to the Sun. Within the uncertainities in the space motion of the Geminga pulsar, about 8 times as many trajectories lead back to the Orion association as lead back to the Local Bubble although both of these have similar volumes. She points out that the expansion age of the Trapezium sub-association is 300,000 years which is comparable to the 340,000-year spin-down age of the Geminga pulsar. She also suggests that the "Orion's Cloak" nebula might be the remnant of the supernova. Radio Observations of Nova Cygni 1992 P E Pavelin et al (Nature, 363, 424-426, 1993) have used the MERLIN radio telescope array to study Nova Cygni 1992. The structure of the expanding shell was first resolved 80 days after the outburst. This is much earlier than the shell would be detectable in optical telescopes. They explain the observed temperatures in the shell as being due to the heating of the gas in shocks produced by the thermonuclear runaway. At one point in their paper, they use Guy Hurst's light-curve published in the October 1992 issue of Astronomy Now to determine the apparent magnitude of the nova 15 days after maximum (6.5).